<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    div{
      width: 200px;
      height: 100px;
      background-color: red;
      /*元素内容居中*/
      text-align: center;
        /*块级元素当前行居中*/
        margin: 0 auto;
    }
    hi{
        margin-bottom: 0;
    }
    p{
        margin-top: 0;
    }
  </style>
</head>
<body>
<div>测试文本</div>
<h1>内容标题</h1>
<p>段落标签p</p>
<ul>
    <li>刘备</li>
    <li>关羽</li>
    <li>张飞</li>
</ul>
</body>
</html>